The present invention relates to a wireless microphone system having a wireless microphone and a receiver unit with a mute circuit and particularly to a receiver unit having function of advancing or delaying timing during a predetermined time interval in switching off or on a mute circuit.
A wireless microphone transmits electric wave containing an audio signal to a receiver unit. The receiver unit often produces noise, because no audio signal is sent from the wireless microphone to the receiver unit, or the audio signal is not received well. For this reason, the receiver unit is provided with a mute circuit (in other words, a squelch circuit) for turning down volume of the audio signal when a noise signal is caused.
The electric wave from the wireless microphone contains an audio signal, a tone signal, and a noise signal. In the conventional receiver unit, the mute circuit was switched on or off by comparison of parameter signals for determining receiving conditions of electric wave with thresholds (reference values), respectively. The parameter signals include a tone signal, noise signal, and signal level of the received electric wave.
The receiver unit includes a tone signal detection circuit for detecting the tone signal, a noise detection circuit for detecting the noise signal, and a signal level detection circuit for detecting the signal level. The signal detection circuit, noise detection circuit, and signal level detection circuit each include comparator circuits having a predetermined threshold. As an example, in the signal level detection circuit, when the signal level fell below the threshold, the comparator circuit outputted a mute signal to the mute circuit.
As above described, in the conventional mute circuit, all of the signal detection circuit, noise detection circuit, and signal level detection circuit require the comparator circuits, and therefore the construction of the mute circuit is large-sized, and the cost for production of the mute circuit inevitably raises. In addition, since the respective parameter signals have different thresholds. This requires setting the threshold values in the respective comparator circuit. It is difficult to regulate the different thresholds in the respective signals.
Furthermore, when the wireless microphone system is actually operated, the wireless microphone unit (transmitter) was switched on, after the receiver has been switched on, and started to stand by. After the wireless microphone was switched on, electric power was fed thereto rapidly. For this reason, when the wireless microphone has started the operation, the variance in the field intensity was caused, and the transmission frequency was stabilized after short time passed. At that time the receiver unit caused noise.
After the wireless microphone was switched on, the comparator circuits closed the mute circuit until the signal level as the parameter signal had reached. When the signal level reached the threshold, the comparator circuits opened the mute circuit. The conventional receiver unit had an analog timing setting circuit that was connected with the output of the comparator circuits for giving a predetermined time delay in a timing of the output of the mute signal from the comparator circuits to the mute circuit such that after the signal level exceeds (raises over or falls below) a predetermined threshold, the mute signal is outputted from the receiver unit to the mute circuit. As a result, when the noise as above described was caused by the extreme variance in the field intensity, it was not outputted from the receiver unit to an external apparatus.
The conventional receiver unit with the analog timing setting circuit provided therein, had problems of which when required, the mute circuit wasn""t switched on. For instance, when a speaker gave a speech with the wireless microphone, a noise signal was generated under the influence of electrical (RF) interference, and thus the signal level fell below a threshold. The mute signal inputted to the mute circuit after an short interval from the time when the signal level had reached the threshold.
In order to solve the above problems, an object of the present invention is to provide a receiver unit for wireless microphone system having a function of controlling the mute circuit. The receiver unit provides a simplified circuitry, and enables to easily set a threshold with respect to the respective parameter signals and to delay or advance timing in switching on/off the mute circuit in accordance with receiving conditions of electric wave.
To accomplish the above object, there is provided a receiver unit for wireless microphone which includes a receiver device for receiving electric wave to be outputted therefrom, a detector circuit connected with the receiver device so as to detect a signal level (field intensity), a tone signal detection circuit connected with the detector circuit through a filter so as to detect a tone signal from the received electric wave, a noise detection circuit connected with the detector circuit through a filter so as to detect a noise signal from the received electric wave, each of the signal level, tone signal, and noise signal being used as parameter signals for detecting received state of the electric wave, a mute circuit which is controlled in accordance with the detected, received state of the electric wave so as to turn down volume of an audio signal, A/D converters for converting the respective parameter signals from analog signals into digital signals, and a controller having threshold to be set with respect to each of the parameter signals, the controller switching off or on the mute circuit in accordance with difference between the parameter signals and threshold.
In a preferred practice the controller provides an instant control of the mute circuit, such that where the parameter signals are high (or low) relative to the threshold value during a predetermined time T1 and thereafter its state is inverted, a predetermined time T2 delay is given in the control of the mute circuit from the inverted time, and where the parameter signals returns to the threshold from the higher level (or lower level) and thereafter its state is inverted.
Thus, the delay control time of the mute circuit that is required to switch on a wireless microphone, for example, is different from the control time of the mute circuit that is required to operate the wireless microphone.
The parameter signals for controlling the mute circuit are selected from the tone and noise signals, and signal level, in which one or all of them may be set as parameter signals. Its combination is of optional.
When the tone signal or signal level for controlling the receiver is set as a parameter signal, an audio signal is turned down in response to that the tone signal or signal level is input at low level relative to the threshold value thereof. In addition, the mute circuit is switched off in response to that the tone signal or signal level as the respective parameter signal is input. As a result, the muting is canceled.
Whereas, if the noise signal is set as a parameter signal, the muting is performed in response to the noise produced at high level relative to the threshold value, and canceled in response to the noise produced at low level relative to the threshold value.
Preferably, the controller comprises a central processing unit (CPU) or micro processor unit (MPU). More specifically, such the controller is of an one-chip microcomputer or one chip microprocessor. In the controller, the threshold value can be input by the simple method of, e.g., pressing keys on a console thereof. Thus, the circuitry of controller is simplified very much.
The receiver unit may have a plurality of A/D converters or a single AD converter. More specifically, each of the tone signal detection circuit, noise signal detection circuit, and signal level detection circuit may have an A/D converter. Alternatively, each of the parameter signals of the tone signal detection circuit, noise detection circuit, and signal level detection circuit may be sequentially converted in time series into digital signals from analog signals by an A/D converter.